Bladder vent plugs for composite-manufacturing bladders and systems and methods for assembling stiffened composite structures

ABSTRACT

Systems (100) for assembling stiffened composite structures comprise a layup mandrel (102) and a network (104) of fluid lines (116) configured to be selectively and fluidically coupled to stringer bladders (118) positioned relative to the layup mandrel (102). Bladder vent plugs (300) are adjustable in length andare configured to close stringer bladders (118) except for fluid connection to the fluid lines (116).

RELATED APPLICATION

The present application is a continuation-in-part of and claims priorityto U.S. patent application Ser. No. 17/857,918, which was filed on Jul.5, 2022, which is entitled “SYSTEMS AND METHODS FOR ASSEMBLING STIFFENEDCOMPOSITE STRUCTURES,” the complete disclosure of which is herebyincorporated by reference.

FIELD

The present disclosure relates to systems and methods of assemblingstiffened composite structures and bladder vent plugs forcomposite-manufacturing bladders.

BACKGROUND

Stiffened composite structures are structures that are constructed ofcomposite materials, such as fiber reinforced composite materials, andtypically include some form of structural frame that carries a skin.Some modern aircraft fuselages are examples of stiffened compositestructures that include a skin operatively coupled to frame members thatextend circumferentially around and that are spaced longitudinally alongthe inside of the fuselage and stringers that extend longitudinallyalong the inside of the fuselage and that are spaced circumferentiallyaround the inside of the fuselage. Stiffened composite fuselages may beconstructed utilizing an inner mold line layup mandrel that includesstringer cavities, or forms, that extend longitudinally along themandrel. Typical stringers, such as hat-shaped stringers, definecavities themselves, with these cavities needing to be filled with astructure that will result in a flush surface to which the skin may beapplied. These filler structures often are referred to as stringermandrels or stringer bladders. Some stringer bladders are solid and madeof a rubber or similar material. Other stringer bladders are hollow.Once the skin is applied over the stringers and the stringer bladders onthe inner mold line layup mandrel, the stringers and skin arevacuum-compacted and co-cured in an autoclave. The vacuum compactingprocess utilizes a flexible sheet of material and sometimes caul platesthat collectively extend across the stringers and skin and are sealed tothe inner mold line layup mandrel around the outer perimeter of thestringers and skin. A vacuum is then applied between the sheet ofmaterial and the inner mold line layup mandrel to compact the stringersand skin together. When hollow stringer bladders are used, the internalvolumes of the stringer bladders must be isolated from the vacuum andfluidically open to atmosphere to avoid the string bladders collapsingduring the vacuum compacting process. This vacuum compacting process isreferred to in the aerospace industry as “bagging” and is labor and timeintensive. In particular, the integrity of the seal between the flexiblesheet of material and the inner mold line layup mandrel is critical.Conventionally, the sheet of material, or “bag,” is perforated by thevent lines that are connected to the internal volumes of the stringerbladders, resulting in numerous potential leak points.

Furthermore, it is important that the stringer bladders fill an entiretyof the stringer cavities of the inner mold line layup mandrel.Conventional stringer bladders utilized in the vacuum compacting processare known to shrink during the vacuum curing process and over thelifetime of the bladder. For example, conventional stringer bladders maycontract in response to changes in pressure and temperature that occurduring the curing process. Shrinking of the bladder (e.g., longitudinalshrinking) may cause the bladder to not completely fill the cavity ofthe stringer creating a void in the cavity. This may result in a failureduring the vacuum compacting process.

SUMMARY

Systems for assembling stiffened composite structures comprise a layupmandrel and a network of fluid lines configured to be selectively andfluidically coupled to stringer bladders relative to the layup mandrel.In some examples, the network of fluid lines extends through the layupmandrel. Some systems further comprise one or more covers configured tobe operatively coupled to the layup mandrel to define a passageextending along the layup mandrel, such that the network of fluid linesis positioned at least partially within the passage when the one or morecovers are operatively coupled to the layup mandrel.

Bladder vent plugs for composite-manufacturing bladders comprise a mainbody defining a main-body bore extending longitudinally through the mainbody and a plug head defining a plug-head bore extending longitudinallythrough the plug head and longitudinally aligned with the main-bodybore. The plug head is configured to be operatively coupled to acomposite-manufacturing bladder. An elongate conduit extends from theplug head and the elongate conduit is slidingly received within themain-body bore. The main-body bore, the plug-head bore, and the elongateconduit are fluidically coupled and collectively define a vent passageextending through the bladder vent plug.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a stiffened compositestructure in the form of an aircraft.

FIG. 2 is an isometric view of an example of a stiffened compositestructure in the form of a barrel section of an aircraft.

FIG. 3 is a representation of an example inner mold line layup mandrelfor assembling a barrel section of an aircraft.

FIG. 4 is a schematic diagram representing systems for assemblingstiffened composite structures.

FIG. 5 is an isometric view of a portion of an example of a system forassembling stiffened composite structures, shown in a cureconfiguration.

FIG. 6 is another isometric view of the portion of the example system ofFIG. 5 , shown in a bladder leak test configuration.

FIG. 7 is another isometric view of a portion of the example system ofFIG. 5 , shown in a manifold leak test configuration.

FIG. 8 is another isometric view of a portion of the example system ofFIG. 5 , shown in a configuration with one stringer and bladder absent.

FIG. 9 is a flowchart schematically representing methods of assemblingstiffened composite structures.

FIG. 10 is a schematic diagram representing bladder vent plugs forcomposite-manufacturing bladders.

FIG. 11 is an exploded view of an example bladder vent plug forcomposite-manufacturing bladders.

FIG. 12 is a top view of the bladder vent plug of FIG. 11 disposed in afirst position.

FIG. 13 is a top view of the bladder vent plug of FIG. 11 disposed in asecond position.

FIG. 14 is a side view of the bladder vent plug of FIG. 11 .

DESCRIPTION

Systems and methods for assembling stiffened composite structures aredisclosed herein. In FIG. 1 , an example of an apparatus 10 that may beconstructed from stiffened composite structures 12 is provided in theform of an aircraft 14; however, other apparatuses 10 are within thescope of the present disclosure, and the present disclosure is notlimited to aircraft and aircraft applications. For example, otherapparatuses 10 that may be constructed of stiffened composite structures12 include (but are not limited to) spacecraft, watercraft, landvehicles, wind turbines, structural towers and masts, etc. Moreover,aircraft 14 may take any suitable form, including commercial aircraft,military aircraft, private aircraft, or any other suitable aircraft.While FIG. 1 illustrates aircraft 14 in the form of a fixed wingaircraft, other types and configurations of aircraft are within thescope of aircraft 14 according to the present disclosure, including (butnot limited to) helicopters and other rotorcraft.

Aircraft 14 include a fuselage 16, which generally corresponds to themain body of the aircraft 14 for holding passengers, crew, cargo, and/orequipment, for example, depending on the particular configuration and/orfunction of an aircraft 14. Typically, although not required, thefuselage 16 of an aircraft 14 is elongate and somewhat cylindrical ortubular. In some embodiments, the fuselage 16 may be constructed ofmultiple sections 18 that are longitudinally spaced along the fuselage16 and operatively coupled together to define the fuselage 16. As usedherein when referencing an aircraft 14, a fuselage 16, and/or acorresponding stiffened composite structure 12, the longitudinaldirection refers to the fore-aft direction, corresponding to alongitudinal, or long, axis, of the fuselage 16. Additionally, the terms“inner” and “outer” when used in connection with an aircraft 14, afuselage 16, and/or a corresponding stiffened composite structure 12refer to the radially inward side and the radially outward side,respectively, of the corresponding stiffened composite structure.Accordingly, the outer side of a fuselage 16 or a component part thereofgenerally faces away from the fuselage 16, and the inner side of afuselage 16 or a component part thereof generally faces the internalvolume that is defined by the fuselage 16. Similar relative terms may beused with respect to stiffened composite structures 12 other thanfuselages 16 and with respect to apparatuses 10 other than aircraft 14.

In FIG. 1 , five fuselage sections 18 are indicated schematically,including a nose and tail section; however, any number or size and shapeof sections 18 may be used to construct a fuselage 16. Sections 18additionally or alternatively may be referred to as barrel sections 18of a fuselage 16, with each barrel section 18 generally defining alength of the fuselage 16. Additionally or alternatively, asschematically illustrated in FIG. 1 , a section 18 may include, or beconstructed of, more than one subsection 20. In the schematicallyillustrated and optional example of FIG. 1 , a section 18 is shownschematically and optionally to include an upper subsection 20 and alower subsection 20; however, a section 18 may be constructed of anysuitable number, configuration, and placement of subsections 20,including no subsections 20 at all.

Aircraft 14 also may include wings 22, horizontal stabilizers 24, and avertical stabilizer 26, each of which may be constructed as a unitarystructure or in subsections that are subsequently assembled together.One or more of a fuselage 16, a fuselage section 18, a fuselagesubsection 20, a wing 22, a horizontal stabilizer 24, a verticalstabilizer 26, or a structural subsection thereof may be constructed ofand/or may be described as a stiffened composite structure 12 accordingto the present disclosure.

Stiffened composite structures 12 according to the present disclosuregenerally encompass structures that are defined by a structural frame 28and a skin 30 that is operatively coupled to and supported by thestructural frame 28. FIG. 2 depicts an illustrative, non-exclusiveexample of a stiffened composite structure 12 in the form of a barrelsection 18 of a fuselage 16 of an aircraft 14. The skin 30 may bedescribed as defining the outer shape of the fuselage 16. As indicatedin FIG. 2 , structural frames 28 include a plurality of stiffeners 32operatively coupled to the inner side of the skin 30. In the example offuselage 16, the stiffeners 32 include a plurality of frame members, orframes, 34 that are operatively coupled to and that extendcircumferentially around the inner side of the skin 30 and that arespaced longitudinally along the fuselage 16. The stiffeners 32 alsoinclude a plurality of stringers 36 that are operatively coupled to andthat extend longitudinally along the inner side of the skin 30 and thatare spaced circumferentially around the fuselage 16. In some embodimentsof stiffened composite structures 12, although not required, the skin 30may be constructed of a plurality of skin segments 38 that collectivelydefine the skin 30, or at least a portion of the skin 30 of a stiffenedcomposite structure 12.

FIG. 3 schematically illustrates an example of a layup mandrel 102 thatmay be used to assemble stiffened composite structures 12. In theillustrated example, the layup mandrel 102 may be described ascomprising an outer surface 106 that defines a plurality of spaced-apartstringer forms 108 that extend longitudinally along the outer surface106, with each stringer form 108 having an outer surface thatcorresponds to one side of a respective stringer 36 that is to be loadedinto the stiffener form 108. Each stringer form 108 also has an open end110. The outer surface 106 of the layup mandrel 102 may be described asdefining a primary skin contour 148 between the stringer forms 108 andthat ultimately shapes the skin 30 of the stiffened composite structure12 being assembled on the layup mandrel 102. The schematicallyrepresented example layup mandrel 102 of FIG. 3 is configured forassembling a cylindrical or other tubular structure, such as barrelsection 18 of a fuselage 16 of an aircraft 14; however, layup mandrels102 may take any suitable configuration depending on the construction ofthe stiffened composite structure 12 being assembled. The example layupmandrel 102 of FIG. 3 may be described as an inner mold line layupmandrel, because the layup mandrel 102 is used to form the stiffenedcomposite structure 12 on a radially outward surface thereof; however,outer mold line layup mandrels also may be used in some systems andmethods according to the present disclosure. Again, the example of FIG.3 is provided as an example only.

Turning now to FIG. 4 , systems 100 for assembling stiffened compositestructures 12 are schematically represented. Generally, in FIG. 4 ,elements that are likely to be included in a given example areillustrated in solid lines, while elements that are optional to a givenexample are illustrated in broken lines. However, elements that areillustrated in solid lines are not essential to all examples of thepresent disclosure, and an element shown in solid lines may be omittedfrom a particular example without departing from the scope of thepresent disclosure. As shown, systems 100 generally comprise at least alayup mandrel 102 and a network 104 of fluid lines 116. The network 104of fluid lines 116 is configured to be selectively and fluidicallycoupled to stringer bladders 118 that are positioned relative to thelayup mandrel 102.

Fluid lines 116 also may be referred to as pipes, piping, tubes, tubing,and the like. In some examples, the network 104 of fluid lines 116 isconfigured to be selectively and fluidically coupled to hollow stringerbladders 118 that are positioned relative to the layup mandrel 102. Inparticular, in some such examples, the network 104 of fluid lines 116 isfluidically open to atmosphere 120 so that internal volumes 136 of thestringer bladders 118, when fluidically coupled to the network 104 offluid lines 116, are fluidically open to atmosphere 120. Accordingly,during a vacuum bagging operation, when a vacuum is drawn between aflexible sheet of material 154 and the layup mandrel 102, the hollowstringer bladders 118 will not collapse.

In some examples, and as schematically illustrated in FIG. 4 , thenetwork 104 extends through, or penetrates, the layup mandrel 102. Byextending through the layup mandrel 102, the network 104 may be open toatmosphere 120 without effecting the vacuum during a vacuum baggingoperation. In particular, the outer surface of the portion of thenetwork 104 that penetrates the layup mandrel 102 (e.g. an outer surfaceof a fluid line 116) may be sealed with the layup mandrel 102 to ensurethe integrity of the vacuum during a vacuum bagging operation. In thismanner, there is no need for the fluid lines 116 to penetrate theflexible sheet of material 154, thereby avoiding perforations andpossible leak points that would otherwise affect the integrity of thevacuum during a vacuum bagging operation. As a result, technician timefor installation of a vacuum bagging system is reduced and the need forrework associated with perforating the flexible sheet of material 154 isavoided. In addition, the flexible sheet of material 154 may be reusednumerous times, unlike with conventional vacuum bagging systems.

In some examples, the network 104 of fluid lines 116 may be described ascomprising one or more subnetworks 119 of the fluid lines 116. In suchexamples, each subnetwork 119 is configured to be selectively andfluidically coupled to more than one of the stringer bladders 118 thatare positioned within the stringer forms 108 of the layup mandrel 102 sothat the stringer bladders 118 are fluidically open to atmosphere 120.In some such examples, each subnetwork 119 comprises a main line 121 anda plurality of jumper lines 122 that extend from the main line 121. Themain line 121 also may be referred to or described as a manifold 121.Each jumper line 122 is configured to extend to a respective stringerbladder 118 that is positioned relative to the layup mandrel 102. Insome such examples, each jumper line 122 comprises a bladder-side jumperquick-connect fitting 124 that is configured to be operatively coupledto a corresponding bladder quick-connect fitting 126 of a respectivebladder 118 of the plurality stringer bladders 118. In particular, eachbladder 118 may comprise a bladder vent plug 158 positioned at aterminal end of the bladder 118 and that effectively closes the hollowinterior of the bladder 118 but for the connection to a vent line, suchas a jumper line 122 via a quick-connect fitting assembly between thejumper line 122 and bladder vent plug 158.

Similarly, in some examples, each jumper line 122 may comprise amanifold-side jumper quick-connect fitting 125, and the main line 121may comprise a main-line quick-connect fitting 127 for each of theplurality of jumper lines 122 and configured to be selectively andrepeatedly coupled to and uncoupled from a respective manifold-sidejumper quick-connect fitting 125.

In some systems 100 that comprise subnetworks 119, the main line 121extends through the layup mandrel 102 and is open to atmosphere 120. Insuch examples, the main line 121 may be described as a vent line 140.

In some examples, the layup mandrel 102 may comprise a face sheet 138,and each subnetwork 119 comprises a vent line 140 that is fluidicallycoupled to a respective main line 121 and that extends through the facesheet 138.

With continued reference to FIG. 4 , some systems 100 further comprise aleak test kit 128 for leak testing the network 104 of the fluid lines116, a subnetwork 119 of the fluid lines 116, and/or the stringerbladders 118. For example, the leak test kit 128 may comprise a gauge130, a plurality of jumper-line caps 132, and an on/off valve 134. Thegauge 130 is configured to be selectively coupled to a respectivesubnetwork 119 and may be a pressure gauge, a flow meter, or any othersuitable mechanism capable of detecting a flow of fluid or change inpressure. The jumper-line caps 132 are configured to be selectivelycoupled to the plurality of jumper lines 122 to isolate the respectivesubnetwork 119 from atmosphere 120. The on/off valve 134 is associatedwith the gauge 130 and is configured to be operatively coupled to asource 133 of pressurized gas 146. Accordingly, the leak test kit 128 isconfigured to selectively couple to a subnetwork 119 to test thepressure integrity of the respective subnetwork 119. More specifically,the ends of the jumper lines 122 of a subnetwork 119 that are configuredto be operatively coupled to the stringer bladders 118 are capped withthe jumper-line caps 132, the gauge 130 and on/off valve 134 are coupledto the main line 121 or a vent line 140 of a subnetwork, and the source133 of pressurized gas 146 is connected to the on/off valve 134. Whenthe on/off 134 valve is turned on, the pressurized gas 146 willpressurize the respective subnetwork 119. Then the on/off valve 134 isclosed, and the gauge 130 is monitored to detect any leaks throughoutthe subnetwork 119.

As schematically represented in FIG. 4 , some systems 100 furthercomprise one or more covers 112 that are configured to be operativelycoupled to the layup mandrel 102 to define a passage 114 extending alongthe layup mandrel 102. In such systems 100, the network 104 of fluidlines 116 is positioned at least partially within the passage 114 whenthe one or more covers 112 are operatively coupled to the layup mandrel102. The cover(s) 112 and the creation of the passage 114 along the openends 110 of the stringer forms 108 may serve at least two purposes.First, the passage 114 provides a volume of space where componentsassociated with the layup mandrel 102, such as the network 104 of fluidlines 116, and the assembly of stiffened composite structures 12 may bepositioned and protected or otherwise shielded, such as from beingengaged by a flexible sheet of material 154 of a vacuum bagging system144. Stated differently, the cover(s) 112 may protect the flexible sheetof material 154 from engagement with components positioned within thepassage 114, thereby avoiding undesirable wear and tear on the flexiblesheet of material 154, and resulting in a longer use life of theflexible sheet of material 154.

In some examples, as schematically represented in FIG. 4 , the cover(s)112 may comprise a smooth outer surface 141 that is suitable tointerface with the flexible sheet of material 154 of a vacuum baggingsystem 144. In other words, not only do the cover(s) 112 protect theflexible sheet of material 154 from the components within the passage114, but the cover(s) 112 themselves may be configured to avoidundesirable wear and tear of the flexible sheet of material 154. Thatis, the cover(s) 112 may not have any sharp edges or corners that arepositioned to engage the flexible sheet of material 154 during a vacuumbagging operation. As a result, the flexible sheet of material 154 maybe reused numerous times without replacement, unlike with conventionalvacuum bagging systems.

In systems 100, whose layup mandrel 102 is an inner mold line layupmandrel with a plurality of stringer forms 108 with open ends 110, theone or more covers 112 are configured to cover the open end 110 of eachstringer form 108, such that the passage 114 extends transverse to theplurality of spaced-apart stringer forms 108. The cover(s) 112 and thelayup mandrel 102 may have any suitable coupling mechanism or componentsoperative to permit for the selective coupling of the cover(s) 112 tothe layup mandrel 102 and for the selective uncoupling, or removal, ofthe cover(s) 112 from the layup mandrel 102. Examples of couplingmechanisms or components include magnets, fasteners, clips, and thelike.

In some examples, the smooth outer surface 141 of the cover(s) comprisesa first region 150 that is parallel to the primary skin contour 148 whenthe cover(s) 112 are operatively coupled to the layup mandrel 102.Accordingly, as schematically illustrated in FIG. 4 , a flexible sheetof material 154 of a vacuum bagging system 144, when operativelyinstalled, may smoothly transition from the first region 150 to a skinsegment 38 or to an optional caul structure 156 that is placed over askin segment 38 during a vacuum bagging operation of a stiffenedcomposite structure 12. In some examples, the cover(s) 112 may bedescribed as being rigid, so as to define the passage 114 when thecover(s) 112 are operatively coupled to the layup mandrel 102. Thecover(s) 112 may be constructed of any suitable material, includingplastics, fiber-reinforced plastics, metal, etc. In some examples, thecover(s) 112 may be constructed of the same material as the outersurface 106 of the layup mandrel 102.

In the example of a system 100 utilized to construct a stiffenedcomposite structure 12 that is cylindrical or tubular, such as a barrelsection 18 of a fuselage 16, the first region 150 therefore may becylindrical or tubular. In some examples, the smooth outer surface 141of the cover(s) 112 also comprises a second region 152 that extends atan angle from the first region 150. In some such examples, the secondregion 152 may be frustoconical.

With continued reference to FIG. 4 , some systems 100 further comprise anetwork 104 of fluid lines 116 that are positioned at least partiallywithin the passage 114 when the cover(s) 112 are operatively coupled tothe layup mandrel 102.

With continued reference to FIG. 4 , systems 100 may be described in astate of use. That is a system 100 may be described as comprising aplurality of stringers 36 and a skin segment 38 operatively positionedrelative to the layup mandrel 102, and a plurality of stringer bladders118 that are positioned within at least a subset of the plurality ofstringers 36. Further, when in use, systems 100 that comprise cover(s)112, the cover(s) 112 are operatively coupled to the layup mandrel 102,and the system 100 further comprises a vacuum bagging system 144 that isoperatively installed relative to the layup mandrel 102 to compact theplurality of stringers 36 and the skin segment 38 together. Inparticular, in some such systems 100, the vacuum bagging system 144comprises a flexible sheet of material 154 that extends over the one ormore covers 112. In some installations of systems 100, the cover(s) 112do not engage the stringers 36 and the skin segment 38.

Turning now to FIGS. 5-8 , an illustrative non-exclusive example ofsystems 100 is illustrated in the form of a system 250. Whereappropriate, the reference numerals from the schematic illustration ofFIG. 4 are used to designate corresponding parts of system 250; however,system 250 is non-exclusive and does not limit systems 100 to theillustrated embodiment of FIGS. 5-8 . That is, systems 100 mayincorporate any number of the various aspects, configurations,characteristics, properties, etc. of systems 100 that are illustrated inand discussed with reference to the schematic representations of FIG. 4and/or the embodiments of FIGS. 5-8 , as well as variations thereof,without requiring the inclusion of all such aspects, configurations,characteristics, properties, etc. For the purpose of brevity, eachpreviously discussed component, part, portion, aspect, region, etc. orvariants thereof may not be discussed, illustrated, and/or labeled againwith respect to system 250; however, it is within the scope of thepresent disclosure that the previously discussed features, variants,etc. may be utilized with system 250.

FIG. 5 illustrates system 250 with three covers 112 operatively coupledto a layup mandrel 102 in the form of an inner mold line layup mandrelwith a plurality of spaced-apart stringer forms 108. The example layupmandrel may be described as a segmented layup mandrel with a joint linethat coincides at a stringer form 108. For clarity, in FIG. 5 , thecorresponding stringers 36 and skin segment(s) 38 that would becompacted utilizing the illustrated system 250 are not shown. Inparticular, system 250 comprises two subnetworks 119 of fluid lines 116.A first subnetwork 252 comprises a main line 121, two jumper lines 122,and two vent lines 140. A second subnetwork 254 comprises a main line121, three jumper lines 122, and two vent lines 140.

FIG. 6 illustrates system 250 but with the covers 112 removed from thelayup mandrel 102 and with a leak test kit 128 installed on thesubnetwork 254. More specifically, a first gauge 130 is installed on oneof the two vent lines 140, and a second gauge 130 with an on/off valve134 is installed on the other of the two vent lines 140 with a source133 of pressurized gas 146 coupled thereto. The jumper lines 122 of thesubnetwork 254 are connected to the respective stringer bladders 118.Accordingly, the subnetwork 254 and the associated stringer bladders 118are pressurized. When the on/off valve 134 is closed, the gauges 130 maybe monitored to determine if any leaks are present.

FIG. 7 illustrates a portion of system 250 comprising the subnetwork254, again with the covers 112 removed from the layup mandrel 102 andwith a leak test kit 128 installed on the subnetwork 254. However, incontrast to FIG. 6 , the stringer bladders 118 are not present, andjumper-line caps 132 are operatively coupled to the jumper lines 122.Accordingly, as illustrated, the subnetwork 254, by itself, ispressurized, and when the on/off valve 134 is closed, the gauges 130 maybe monitored to determine if any leaks are present in the subnetwork254.

FIG. 8 again illustrates the portion of system 250 comprising thesubnetwork 254. Again, in FIG. 8 , the covers 112 are moved from thelayup mandrel. Two stringer bladders 118 are present and operativelycoupled to corresponding jumper lines 122. A third jumper line 122 iscapped with a jumper-line cap 132, illustrating that a system 100 may beinstalled and utilized in connection with fewer than the total possiblenumber of stringer bladders 118

FIG. 9 schematically provides a flowchart that represents illustrative,non-exclusive examples of methods 200 according to the presentdisclosure. In FIG. 9 , some steps are illustrated in dashed boxesindicating that such steps may be optional or may correspond to anoptional version of a method according to the present disclosure. Thatsaid, not all methods according to the present disclosure are requiredto include the steps illustrated in solid boxes. The methods and stepsillustrated in FIG. 9 are not limiting and other methods and steps arewithin the scope of the present disclosure, including methods havinggreater than or fewer than the number of steps illustrated, asunderstood from the discussions herein.

Methods 200 of utilizing a system 100 comprise operatively loading 202stringers 36 and a skin segment 38 relative to a layup mandrel 102, andpositioning 204 stringer bladders 118 into stringer cavities of thestringers 36. In methods 200 utilizing an inner mold line layup mandrelwith a plurality of spaced-apart stringer forms 108, the stringers 36are positioned within the stringer forms 108. In some methods 200, thestringers 36 and the stringer bladders 118 may be kitted away from thelayup mandrel 102 and loaded on the layup mandrel 102 together. In othermethods 200, the stringers 36 may be positioned in the stringer forms108 of the layup mandrel 102 before the stringer bladders 118 arepositioned within the cavities of the stringers 36

Methods 200 further comprise fluidically coupling 206 the stringerbladders 118 to a network 104 of fluid lines 116 so that the internalvolumes 136 of the stringer bladders 118 are fluidically open toatmosphere 120, and operatively installing 212 a vacuum bagging system144 relative to the layup mandrel 102, the stringers 36, and the skinsegment 38 that loaded on the layup mandrel 102. Following theoperatively installing 212 the vacuum bagging system 144, methods 200comprise drawing 214 a vacuum on the stringers 36 and the skin segment38 while maintaining atmospheric pressure of the stringer bladders 118via the network 104 of fluid lines 116. Methods 200 further compriseconcurrently with the drawing 214 the vacuum, curing 216 the stringers36 and the skin segment 38.

In methods 200 that utilize a system 100 that comprises one more covers112, such methods 200 also may comprise, following the fluidicallycoupling 206, operatively coupling 208 one or more covers 112 to thelayup mandrel 102 to define a passage 114.

As schematically represented in FIG. 9 , some methods 200 furthercomprise, following the curing 216, uninstalling 218 the vacuum baggingsystem 144 from the layup mandrel 102, and following the uninstalling218, removing 220 the one or more covers 112 from the layup mandrel 102.In addition in such examples of methods 200, following the removing 220the one or more covers 112, methods 200 further comprise disconnecting222 the stringer bladders 118 from the network 104 of fluid lines 116,and removing 224 the stringer bladders 118 from the stringers 36.Following the uninstalling 218, such methods 200 also comprise removing226 the stringers 36 and the skin segment 38 from the layup mandrel 102.

Some methods 200 further comprise prior to the fluidically coupling 206the stringer bladders 118 to the network 104 of fluid lines 116, capping228 the plurality of jumper lines 122 of a respective subnetwork 119,operatively coupling 230 a gauge 130 to the respective subnetwork 119,and pressurizing 232 the respective subnetwork 119 to leak test therespective subnetwork 119.

Some methods 200 further comprise, following the fluidically coupling206 the stringer bladders 118 to the network 104 of fluid lines 116,operatively coupling 234 a gauge 130 to the respective subnetwork 119,and pressurizing 236 the respective subnetwork 119 and the stringerbladders 118 fluidically coupled to the respective subnetwork 119 toleak test the stringer bladders 118 that are fluidically coupled to therespective subnetwork 119.

Turning now to FIG. 10 , bladder vent plugs 300 are schematicallyrepresented. Generally, in FIG. 10 , elements that are likely to beincluded in a given example are illustrated in solid lines, whileelements that are optional to a given example are illustrated in brokenlines. However, elements that are illustrated in solid lines are notessential to all examples of the present disclosure, and an elementshown in solid lines may be omitted from a particular example withoutdeparting from the scope of the present disclosure.

Bladder vent plugs 300 may be utilized with and incorporated intosystems 100 of the present disclosure, but also may be used with othercomposite manufacturing systems. That is, bladder vent plugs 300 areexamples of bladder vent plugs 158, described above. As schematicallyrepresented in FIG. 10 , bladder vent plugs 300 are configured to beutilized with a composite-manufacturing bladder 302. For example, abladder vent plug 300 may be positioned at the terminal end of acomposite-manufacturing bladder 302 to effectively close a hollowinterior 338 of the composite-manufacturing bladder 302 except forconnecting to a vent line. A bladder vent plug 300 may be coupled to acomposite-manufacturing bladder 302 in any suitable manner.

In some examples, composite-manufacturing bladders 302 are hollow,elastomeric composite-manufacturing bladders. Hollow, elastomericcomposite-manufacturing bladders may shrink during the vacuum curingprocess and/or over the lifetime of the bladder. For example, thehollow, elastomeric composite-manufacturing bladder may contract inresponse to pressure and temperature changes that occur during thevacuum curing process. Shrinking of the bladder (e.g., longitudinalshrinking) may cause the bladder to not completely fill the cavity ofthe stringer in which the bladder is disposed, creating a void that mustbe filled to prevent a failure during the vacuum curing process. Bladdervent plugs 300 are configured to be coupled to the hollow, elastomericbladders, and bladder vent plugs 300 are adjustable in length tofacilitate accounting for shrinkage of the hollow, elastomeric bladders.For example, the length of a bladder vent plug 300 may be increased tofill a void in the cavity of the stringer caused by shrinking of acomposite-manufacturing bladder 302. In some examples, the bladder ventplug 300 is configured to automatically adjust in length in response tocontraction of the composite-manufacturing bladder 302 during the vacuumcuring process.

As schematically represented in FIG. 10 , bladder vent plugs 300comprise a main body 304 defining a main-body bore 306 that extendslongitudinally through the main body 304. The main body 304 may compriseany suitable structure(s) defining the main-body bore 306. Bladder ventplugs 300 comprise a plug head 308 defining a plug-head bore 310 thatextends longitudinally through the plug head 308. The plug head 308 maycomprise any suitable structure(s) defining the plug-head bore 310. Theplug head 308 and the main body 304 are arranged such that the plug-headbore 310 is longitudinally aligned with the main-body bore 306.

The plug head 308 is configured to be operatively coupled to thecomposite-manufacturing bladder 302, as shown in FIG. 10 . The plug head308 may comprise any suitable structure(s) configured to be coupled tothe composite-manufacturing bladder 302 and the plug head 308 may becoupled to the composite-manufacturing bladder 302 in any suitablemanner. In some examples, the plug head 308 effectively closes a hollowinterior 338 of the composite-manufacturing bladder 302 except for fluidcommunication between the plug-head bore 310 and the hollow interior 338of the composite-manufacturing bladder 302.

The bladder vent plug 300 comprises an elongate conduit 312 extendingfrom the plug head 308. The elongate conduit 312 extends into and isslidingly received within the main-body bore 306 of the main body 304.The elongate conduit 312 may comprise any suitable structure(s)configured to be slidingly received within the main-body bore 306. Forexample, the elongate conduit 312 may comprise a hollow annular rod, andthe main-body bore 306 may comprise an annular bore. In some examples,the main-body bore 306, the plug-head bore 310, and the elongate conduit312 are each annular. The main-body bore 306, the plug-head bore 310,and the elongate conduit 312 are each longitudinally aligned with eachother.

In some examples, as schematically represented in FIG. 10 , themain-body bore 306 comprises a main portion 307 that is longitudinallyaligned and coaxial with the elongate conduit 312 and within which theelongate conduit 312 is slidingly received, and a transverse exitportion 309 that extends transverse (e.g., perpendicular to) to the mainportion 307. In some such examples, the transverse exit portion 309 ofthe main-body bore 306 exits a lateral side of the main body 304, suchas schematically represented in the upper right corner of FIG. 10 . Inother examples, the transverse exit portion 309 of the main-body bore306 exits a top or bottom surface of the main body 304, such asschematically represented by the dashed circle at the right end of FIG.10 . In some such examples, the transverse exit portion 309 ispositioned to communicate with a corresponding vent bore (e.g., ventline 140) that passes through a face sheet 138 of a layup mandrel 102,such as schematically and optionally illustrated in FIG. 4 . In somesuch examples, the transverse exit portion 309 may extend fully throughthe main body 304, and a banjo fitting, or other style of vent plug, maybe utilized to plug the portion of the transverse exit portion 309 thatis opposite the vent bore of the layup mandrel 102.

The elongate conduit 312 couples the main body 304 to the plug head 308,such that a distance between the main body 304 and the plug head 308 maybe adjusted by sliding the elongate conduit 312 within the main-bodybore 306. Adjusting the distance between the main body 304 and the plughead 308 adjusts an overall longitudinal length of the bladder vent plug300. The adjustable longitudinal length of the bladder vent plug 300facilitates accommodating for composite-manufacturing bladders that haveshrunk in length or that contract in length during use (e.g., during thevacuum curing process), such that the bladder no longer completely fillsa cavity of the stringer in which the bladder is disposed. For example,the bladder vent plug 300 may be extended in length to fill a void in acavity of a stringer in which the composite-manufacturing bladder 302 isdisposed. In some examples, the bladder vent plug 300 is configured toautomatically adjust in length in response to contraction of thecomposite-manufacturing bladder 302 during the curing process.

The main-body bore 306, the plug-head bore 310, and the elongate conduit312 are fluidically coupled to each other and collectively define a ventpassage 314 extending through bladder vent plug 300. In some examples,the vent passage 314 is configured to be in fluid communication with thehollow interior 338 of the composite-manufacturing bladder 302. Forexample, the plug head 308 may be configured to close the hollowinterior 338 of the composite-manufacturing bladder 302 except for fluidcommunication between the vent passage 314 and the hollow interior 338.

In some examples, bladder vent plugs 300 comprise a main-body sealingmember 316 coupled to the main body 304 and engaged with the elongateconduit 312. The elongate conduit 312 is configured to translaterelative to the main-body sealing member 316 which may be fixed at anysuitable position of the main-body bore 306. The main-body sealingmember 316 may comprise any suitable component(s) configured to providea seal between the elongate conduit 312 and the main-body bore 306. Themain-body sealing member 316 may comprise any suitable number of sealingmember(s). For example, the main-body sealing member 316 may comprise awiper seal 318 disposed around the main-body bore 306. The wiper seal318 is configured to prevent dirt and debris from entering into themain-body bore 306. Additionally or alternatively, the main-body sealingmember 316 may comprise a main-body O-ring 320 disposed around themain-body bore 306. The main-body O-ring 320 engages the elongateconduit 312 to provide the seal between the main-body bore 306 and theelongate conduit 312.

In some examples, bladder vent plugs 300 comprise an elongate-conduitsealing member 322 coupled to the elongate conduit 312 and engaged withthe main-body bore 306. The elongate-conduit sealing member 322 isconfigured to translate relative to the main-body bore 306 with theelongate conduit 312. For example, the elongate-conduit sealing member322 may be fixed to the elongate conduit 312 at any suitable position,such that the elongate-conduit sealing member 322 moves with theelongate conduit 312 within the main-body bore 306. The elongate-conduitsealing member 322 may comprise any suitable structure(s) configured toprovide a seal between the elongate conduit 312 and the main-body bore306. For example, the elongate-conduit sealing member 322 may comprisean the elongate-conduit 324 disposed around the elongate conduit 312 andconfigured to engage the main-body bore 306. Bladder vent plugs 300 maycomprise any suitable number and/or type of the elongate-conduit sealingmembers 322.

In some examples, bladder vent plugs 300 comprise at least one strokelimiter 326 fixed to the plug head 308. In such examples, the main body304 defines at least one stroke-limiter bore 328 and each stroke limiter326 is slidingly received within a respective stroke-limiter bore 328 ofthe main body 304. The stroke-limiter bore 328 is configured tooperatively restrict the stroke limiter 326 from fully exiting thestroke-limiter bore 328. The stroke limiter 326 may comprise anysuitable component(s) and/or structure(s) configured to be slidinglyreceived within the stroke-limiter bore 328 of the main body 304 andconfigured to be operatively restricted from fully exiting thestroke-limiter bore 328. For example, the stroke limiter 326 maycomprise a shoulder bolt having a threaded end fixed to the plug head308 and a shaft extending into the stroke-limiter bore 328.

In some examples, the stroke-limiter bore 328 defines a shoulder 330and/or any other suitable structure(s) configured to operativelyrestrict the stroke limiter 326 from fully exiting the stroke-limiterbore 328. The stroke limiter 326 may comprise a head 332 and/or anyother suitable structure(s) configured to engage the shoulder 330 tooperatively restrict the stroke limiter 326 from fully exiting thestroke-limiter bore 328. The stroke limiter 326 and the stroke-limiterbore 328 facilitate restricting the plug head 308 from becomingdecoupled from the main body 304 and may limit a maximum extensionlength of the bladder vent plugs 300.

Bladder vent plugs 300 may comprise any suitable number of the strokelimiters 326 each slidingly received within a respective stroke-limiterbore 328 of the main body 304. In the example of FIG. 10 , bladder ventplugs 300 comprise two stroke limiters 326 and two stroke-limiter bores328. The stroke-limiter bores 328 are disposed on opposing sides of themain-body bore 306 and the stroke limiters 326 are fixed to the plughead 308 on opposing sides of the elongate conduit 312. However, bladdervent plugs 300 may have any suitable number and configuration of thestroke limiters 326 and the stroke-limiter bores 328.

In some examples, bladder vent plugs 300 comprise a vent connector 334coupled to the main body 304. The vent connector 334 is in fluidcommunication with the main-body bore 306. The vent connector 334 is influid communication with the vent passage 314 defined by the main-bodybore 306, the elongate conduit 312, and the plug-head bore 310. The ventplug 300 is configured to provide fluid communication between a fluidline coupled to the vent connector 334 and the hollow interior 338 ofthe composite-manufacturing bladder 302 coupled to the plug head 308 viathe vent passage 314. The vent connector 334 may comprise any suitablecomponent(s) configured to be coupled to a fluid line. In some examples,the vent connector 334 is longitudinally aligned with the elongateconduit 312, which is slidingly received within the main-body bore 306.In some examples, the vent connector 334 is laterally offset from theelongate conduit 312.

In some examples, bladder vent plugs 300 comprise a sleeve 336operatively coupled to the plug head 308 and the main body 304. Thesleeve 336 is disposed between the plug head 308 and the main body 304and extends around the elongate conduit 312. The sleeve 336 may compriseany suitable structure configured to expand and contract when a distancebetween the plug head 308 and the main body 304 is adjusted by slidingthe elongate conduit 312 within the main-body bore 306. The sleeve 336is configured to extend around and cover a portion of the elongateconduit 312 extending between the plug head 308 and the main-body bore306. The sleeve 336 is configured to block dirt and debris from enteringthe main-body bore 306. In some examples, the sleeve 336 is corrugatedand configured to be adjustable in length.

The plug head 308 and the main body 304 may have any suitable sizeand/or cross-sectional shape. In some examples, the main body 304 andthe plug head 308 have an at least substantially similar cross-sectionalshape. Alternatively, the main body 304 may have a first cross-sectionalshape and the plug head 308 may have a second cross-sectional shapedifferent from the first cross-sectional shape of the plug head 308. Insome examples, the composite-manufacturing bladder 302 has an at leastsubstantially similar cross-sectional shape as the plug head 308 and/orthe main body 304. The plug head 308 having a substantially similarcross-sectional shape as the composite-manufacturing bladder 302facilitates the plug head 308 coupling to the composite-manufacturingbladder 302 and closing off the hollow interior 338 of thecomposite-manufacturing bladder 302.

FIGS. 11-14 depict an illustrative bladder vent plug 400 forcomposite-manufacturing bladders, such as composite-manufacturingbladder 302, described above. The bladder vent plug 400 is an example ofbladder vent plugs 300, described above. In some examples, the bladdervent plug 400 is configured to be utilized with hollow, elastomericcomposite-manufacturing bladders. Hollow, elastomericcomposite-manufacturing bladders may shrink over the lifetime of thebladder and/or during the vacuum curing process. Shrinking and/orcontraction of the bladder may cause the bladder to not completely fillthe cavity of the stringer in which the bladder is disposed creating avoid that must be filled to prevent a failure during the vacuum curingprocess. The bladder vent plug 400 is configured to be coupled to thehollow, elastomeric bladder and the bladder vent plug 400 is adjustablein length to facilitate filling voids in the stringer cavity caused byshrinking of the bladder. In some examples, the bladder vent plug 400 isconfigured to automatically adjust in length in response to contractionof the composite-manufacturing bladder that occurs during the curingprocess.

As shown in FIG. 11 , The bladder vent plug 400 comprises a main body404 defining a main-body bore 406. The main-body bore 406 extendslongitudinally through the main body 404. The bladder vent plug 400comprises a plug head 408 defining a plug-head bore 410 that extendslongitudinally through the plug head 408. The plug-head bore 410 and themain-body bore 406 are longitudinally aligned with each other. The plughead 408 is configured to be operatively coupled to acomposite-manufacturing bladder, such as composite-manufacturing bladder302, described above. An elongate conduit 412 extends from the plug head408 and is slidingly received within the main-body bore 406.

The main-body bore 406, the elongate conduit 412, and the plug-head bore410 are fluidically coupled and collectively define a vent passage 414extending through the bladder vent plug 400. When the plug head 408 iscoupled to a composite-manufacturing bladder, the plug head 408operatively closes a hollow interior of the bladder except for fluidcommunication between the plug-head bore 410 and the hollow interior ofthe bladder. The bladder vent plug 400 is configured such that thehollow interior of the bladder coupled to the plug head 408 is in fluidcommunication with the vent passage 414 via the plug-head bore 410.

The main body 404 of the bladder vent plug 400 may have any suitablemain-body sealing members configured to provide a seal between themain-body bore 406 and the elongate conduit 412 that is slidinglyreceived in the main-body bore 406. As shown in FIG. 11 , the main-bodysealing members comprise a wiper seal 418 and a main-body O-ring 420.The wiper seal 418 is coupled to the main body 404 and configured toprovide a seal between the main-body bore 406 and the elongate conduit412. The wiper seal 418 is engaged with the elongate conduit 412 and isconfigured to prevent dirt and debris from entering into the main-bodybore 406 on the elongate conduit 412. The main-body O-ring 420 iscoupled to the main body 404 and engaged with the elongate conduit 412.In some examples, the main-body O-ring 420 is disposed within a grooveformed in the main-body bore 406. Both the wiper seal 418 and themain-body O-ring 420 are fixed to the main body 404, such that theelongate conduit 312 translates relative to the wiper seal 418 and themain-body O-ring 420 within the main-body bore 406.

The elongate conduit 412 of the bladder vent plug 400 may have anysuitable elongate-conduit sealing member(s) configured to provide a sealbetween the elongate conduit 412 and the main-body bore 406. Theelongate-sealing member of the bladder vent plug 400 comprises anelongate-conduit O-ring 424 coupled to the elongate conduit 412, suchthat the elongate-conduit O-ring 424 translates with the elongateconduit 412 relative to the main-body bore 406. The elongate-conduitO-ring 424 engages the main-body bore 406 to provide the seal betweenthe elongate conduit 412 and the main-body bore 406. In some examples,the elongate-conduit O-ring 424 is disposed within a groove formed inthe elongate conduit 412.

The bladder vent plug 400 comprises a vent connector 434 coupled to themain body 404. The vent connector 434 is in fluid communication with themain-body bore 406 and the vent passage 414. The vent connector isconfigured to be coupled to a fluid line (e.g., jumper lines 122 ofsystem 100). The bladder vent plug 400 is configured to provide fluidcommunication between a fluid line coupled to the vent connector 434 andthe hollow interior of the bladder coupled to the plug head 408 via thevent passage 414. The vent connector 434 may comprise any suitablemechanism configured to be coupled to a fluid line. As shown in FIGS. 12and 13 , the vent connector 434 is longitudinally aligned with theelongate conduit 412 and the main-body bore 406. In some examples, thevent connector 434 is laterally offset from the elongate conduit 412.

The bladder vent plug 400 comprises a sleeve 436 coupled to the mainbody 404 and the plug head 408. The sleeve 436 is disposed between themain body 404 and the plug head 408 and the sleeve 436 is configured toexpand or contract when a distance between the main body 404 and theplug head 408 is adjusted. The sleeve 436 is disposed around theelongate conduit 412 extending between the plug head 408 and themain-body bore 406. The sleeve 436 is configured to block dirt anddebris from entering the space between the main body 404 and the plughead 408. The sleeve 436 is corrugated to facilitate expanding andcontracting when the distance between the main body 404 and the plughead 408 is adjusted.

The bladder vent plug 400 comprises a pair of stroke limiters 426 andthe main body 404 defines a pair of stroke-limiter bores 428. Each ofthe stroke limiters 426 is fixed to the plug head 408 and extends intoand is slidingly received within a respective one of the pair ofstroke-limiter bores 428 in the main body 404. The stroke limiters 426may comprise any suitable component(s) configured to be slidinglyreceived within the stroke-limiter bores 428. For example, as shown inFIGS. 11-13 , the stroke limiters 426 each comprise a shoulder bolthaving a threaded end fixed to the plug head 408 and a shank extendinginto the stroke-limiter bore 428. The stroke limiters 426 each comprisea respective head 432 disposed within the stroke-limiter bore 428.

Each stroke-limiter bore 428 defines a shoulder 430 configured tooperatively restrict the stroke limiter 426 from fully exiting thestroke-limiter bore 428. The head 432 of each stroke limiter 426 isconfigured to engage the shoulder 430 to operatively restrict the strokelimiter 426 from fully exiting the stroke-limiter bore 428. As such, thestroke limiters 426 and the stroke-limiter bores 428 are configured tolimit a maximum extension length of the bladder vent plug 400 andconfigured to prevent unwanted decoupling of the plug head 408 from themain body 404. The stroke limiters 426 may have any suitable lengthdependent on the desired maximum length of extension of the bladder ventplug 400.

The bladder vent plug 400 is adjustable in length by sliding theelongate conduit 412 within the main-body bore 406 to change thedistance between the plug head 408 and the main body 404. As describedabove, hollow, elastomeric composite-manufacturing bladders may shrinkduring the lifetime of the bladder. By adjusting in length, the bladdervent plug 400 is able to accommodate bladder shrinkage by filling anyvoids created in the stringer due to the shrinkage of the bladder.

In FIG. 12 the bladder vent plug 400 is extended to a first longitudinallength, and in FIG. 13 the bladder vent plug 400 is extended to a secondlongitudinal length that is greater than the first longitudinal lengthdepicted in FIG. 12 . The elongate conduit 412 slides within themain-body bore 406 between the position shown in FIG. 12 and theposition shown in FIG. 13 . Similarly, the stroke limiters 426 slidewithin the stroke-limiter bores 428 between the position shown in FIG.12 and the position shown in FIG. 13 . As shown in FIGS. 12 and 13 , thehead 432 of each stroke limiter 426 approaches the shoulder 430 of thestroke-limiter bore 428 as the bladder vent plug 400 is extended inlength. The bladder vent plug 400 is able to extend until the head 432of each stroke limiter 426 engages or contacts the shoulder 430 of eachstroke-limiter bore 428. When the head 432 of each stroke limiter 426engages the shoulder 430 of each stroke-limiter bore 428, the bladdervent plug 400 is restricted from extending further in longitudinallength.

As shown in FIG. 14 , the plug head 408 has a cross-sectional shape thatsubstantially matches a cross sectional shape of a stringer in the formof a composite mandrel. This facilitates the bladder vent plug 400fitting within a cavity of the stringer to fill any voids in thestringer cavity caused by shrinkage of the composite-manufacturingbladder to which the vent plug is coupled to. As shown in FIG. 14 , thevent passage 414 formed by the plug-head bore 410, the elongate conduit412, and the main-body bore 406 extends longitudinally through thebladder vent plug 400. The vent passage 414 is configured to providefluid communication between a vent line coupled to the vent connector434 and a hollow interior of a composite-manufacturing bladder coupledto the plug head 408.

Illustrative, non-exclusive examples of inventive subject matteraccording to the present disclosure are described in the followingenumerated paragraphs:

A. A system (100) for assembling stiffened composite structures (12),the system (100) comprising:

-   -   a layup mandrel (102) comprising an outer surface (106); and    -   a network (104) of fluid lines (116), wherein the network (104)        of fluid lines (116) is configured to be selectively and        fluidically coupled to stringer bladders (118) positioned        relative to the layup mandrel (102).

A1. The system (100) of paragraph A, wherein the network (104) of fluidlines (116) is fluidically open to atmosphere (120) so that internalvolumes (136) of the stringer bladders (118), when fluidically coupledto the network (104) of fluid lines (116), are fluidically open toatmosphere (120).

A2. The system (100) of any of paragraphs A-A1, wherein the network(104) of fluid lines (116) extends through the layup mandrel (102).

A3. The system (100) of any of paragraphs A-A2, wherein the network(104) of fluid lines (116) comprises one or more subnetworks (119) ofthe fluid lines (116), wherein each subnetwork (119) of the one or moresubnetworks (119) is configured to be selectively and fluidicallycoupled to more than one of the stringer bladders (118) so that the morethan one of the stringer bladders (118) are fluidically open toatmosphere (120).

A3.1. The system (100) of paragraph A3, wherein each subnetwork (119) ofthe one or more subnetworks (119) comprises a main line (121) and aplurality of jumper lines (122) extending from the main line (121),wherein each jumper line (122) of the plurality of jumper lines (122) isconfigured to be operatively coupled to a respective stringer bladder(118) of the stringer bladders (118).

A3.1.1. The system (100) of paragraph A3.1, wherein each jumper line(122) of the plurality of jumper lines (122) comprises a bladder-sidejumper quick-connect fitting (124) configured to be operatively coupledto a corresponding bladder quick-connect fitting (126) of the respectivebladder (118) of the stringer bladders (118).

A3.1.2. The system (100) of any of paragraphs A3.1-A3.1.1, wherein eachjumper line (122) of the plurality of jumper lines (122) comprises amanifold-side jumper quick-connect fitting (125), and wherein the mainline (121) comprises a main-line quick-connect fitting (127) for eachjumper line (122) of the plurality of jumper lines (122).

A3.1.3. The system (100) of any of paragraphs A3.1-A3.1.2, wherein themain line (121) of each subnetwork (119) of the one or more subnetworks(119) extends through the layup mandrel (102).

A3.1.4. The system (100) of any of paragraphs A3.1-A3.1.3, wherein thelayup mandrel (102) comprises a face sheet (138), wherein eachsubnetwork (119) of the one or more subnetworks (119) further comprisesat least one vent line (140), and wherein each vent line (140) isfluidically coupled to a respective main line (121) through the facesheet (138).

A3.2. The system (100) of any of paragraphs A3-A3.1.4, furthercomprising a leak test kit (128) comprising:

-   -   a gauge (130) configured to be selectively coupled to a        respective subnetwork (119) of the one or more subnetworks        (119);    -   a plurality of jumper-line caps (132) configured to be        selectively coupled to the plurality of jumper lines (122); and    -   an on/off valve (134) associated with the gauge (130) and        configured to be operatively coupled to a source (133) of        pressurized gas (146);    -   wherein the leak test kit (128) is configured to selectively        pressurize the respective subnetwork (119) of the one or more        subnetworks (119) of the fluid lines (116) to test pressure        integrity of the respective subnetwork (119).

A4. The system (100) of any of paragraphs A-A3.2, further comprising:

-   -   one or more covers (112) configured to be operatively coupled to        the layup mandrel (102) to define a passage (114) extending        along the layup mandrel (102);    -   wherein the network (104) of fluid lines (116) is positioned at        least partially within the passage (114) when the one or more        covers (112) are operatively coupled to the layup mandrel (102),        and wherein the network (104) of fluid lines (116) is configured        to be selectively and fluidically coupled to the stringer        bladders (118) when positioned relative to the layup mandrel        (102).

A4.1. The system (100) of paragraph A4, wherein the one or more covers(112) comprise a smooth outer surface (141) suitable to interface with aflexible sheet of material (154) of a vacuum bagging system (144).

A4.2. The system of any of paragraphs A4-A4.1,

-   -   wherein the outer surface (106) of the layup mandrel (102)        defines a plurality of spaced-apart stringer forms (108)        extending longitudinally along the outer surface (106), wherein        each stringer form (108) of the plurality of spaced-apart        stringer forms (108) comprises an open end (110);    -   wherein when the one or more covers (112) are operatively        coupled to the layup mandrel (102), the one or more covers (112)        cover the open end (110) of each stringer form (108) of the        plurality of spaced-apart stringer forms (108), and the passage        (114) extends transverse to the plurality of spaced-apart        stringer forms (108); and    -   wherein the network (104) of fluid lines (116) is configured to        be selectively and fluidically coupled to the stringer bladders        (118) when positioned within the plurality of spaced-apart        stringer forms (108).

A4.2.1. The system (100) of paragraph A4.2 when depending from paragraphA4.1, wherein the outer surface (106) of the layup mandrel (102) definesa primary skin contour (148), and wherein the smooth outer surface (141)of the one or more covers (112) comprises a first region (150) that isparallel to the primary skin contour (148) when operatively coupled tothe layup mandrel (102).

A4.2.1.1. The system (100) of paragraph A4.2.1, wherein the smooth outersurface (141) of the one or more covers (112) comprises a second region(152) that extends at an angle from the first region (150).

A4.2.1.1.1. The system (100) of paragraph A4.2.1.1, wherein the firstregion (150) is cylindrical, and wherein the second region (152) isfrustoconical.

A5. The system (100) of any of paragraphs A-A4.2.1.1.1, furthercomprising:

-   -   a plurality of stringers (36) and a skin segment (38)        operatively positioned relative to the layup mandrel (102); and    -   a plurality of stringer bladders (118) positioned within at        least a subset of the plurality of stringers (36).

A5.1. The system (100) of paragraph A5 when depending from paragraph A4,wherein the one or more covers (112) are operatively coupled to thelayup mandrel (102), and wherein the system (100) further comprisesa/the vacuum bagging system (144) operatively installed relative to thelayup mandrel (102) to compact the plurality of stringers (36) and theskin segment (38).

A5.1.1. The system (100) of paragraph A5.1, wherein the vacuum baggingsystem (144) comprises a/the flexible sheet of material (154) extendingover the one or more covers (112).

A5.1.1.1. The system (100) of paragraph A5.1.1, wherein the fluid lines(116) do not penetrate the flexible sheet of material (154).

A5.1.2. The system (100) of any of paragraphs A5.1-A5.1.1.1, wherein theone or more covers (112) do not engage the plurality of stringers (36)and the skin segment (38).

A6. The system (100) of any of paragraphs A-A5.1.2, wherein the layupmandrel (102) corresponds to at least a portion of a fuselage (16) of anaircraft (14).

A7. The use of the system (100) of any of paragraphs A-A6 to assemblea/the stiffened composite structure (12).

A8. The system (100) of any one of paragraphs A-A6, further comprisingthe bladder vent plug (300) of any one of paragraphs C1-C12.1 configuredto be operatively coupled to a respective one of the stringer bladders(118), such that the bladder vent plug (300) closes the internal volume(136) of the respective stringer bladder (118) except for connection tothe network of fluid lines (116).

B. A method (200) of utilizing the system (100) of any of paragraphsA-A8, the method (200) comprising:

-   -   operatively loading (202) stringers (36) and a/the skin segment        (38) relative to the layup mandrel (102);    -   positioning (204) the stringer bladders (118) into stringer        cavities of the stringers (36);    -   fluidically coupling (206) the stringer bladders (118) to the        network (104) of fluid lines (116) so that the internal volumes        (136) of the stringer bladders (118) are fluidically open to        atmosphere (120);    -   operatively installing (212) a/the vacuum bagging system (144)        relative to the layup mandrel (102), the stringers (36), and the        skin segment (38);    -   following the operatively installing (212) the vacuum bagging        system (144), drawing (214) a vacuum on the stringers (36) and        the skin segment (38) while maintaining atmospheric pressure of        the stringer bladders (118) via the network (104) of fluid lines        (116); and concurrently with the drawing (214) the vacuum,        curing (216) the stringers (36) and the skin segment (38).

B1. The method (200) of paragraph B when depending from paragraph A4,further comprising:

-   -   following the fluidically coupling (206), operatively coupling        (208) the one or more covers (112) to the layup mandrel (102) to        define the passage (114).

B1.1. The method (200) of paragraph B1, further comprising:

-   -   following the curing (216), uninstalling (218) the vacuum        bagging system (144) from the layup mandrel (102);    -   following the uninstalling (218), removing (220) the one or more        covers (112) from the layup mandrel (102);    -   following the removing (220) the one or more covers (112):        -   disconnecting (222) the stringer bladders (118) from the            network (104) of fluid lines (116); and        -   removing (224) the stringer bladders (118) from the            stringers (36); and    -   following the uninstalling (218), removing (226) the stringers        (36) and the skin segment (38) from the layup mandrel (102).

B2. The method (200) of any of paragraphs B-B1.1 when depending fromparagraph A3.1, further comprising, prior to the fluidically coupling(206) the stringer bladders (118) to the network (104) of fluid lines(116):

-   -   capping (228) the plurality of jumper lines (122) of a        respective subnetwork (119);    -   operatively coupling (230) a gauge (130) to the respective        subnetwork (119); and    -   pressurizing (232) the respective subnetwork (119) to leak test        the respective subnetwork (119).

B3. The method (200) of any of paragraphs B-B2 when depending fromparagraph A3.1, further comprising, following the fluidically coupling(206) the stringer bladders (118) to the network (104) of fluid lines(116):

-   -   operatively coupling (234) a/the gauge (130) to the respective        subnetwork (119); and    -   pressurizing (236) the respective subnetwork (119) and the        stringer bladders (118) fluidically coupled to the respective        subnetwork (119) to leak test the stringer bladders (118)        fluidically coupled to the respective subnetwork (119).

B4. The method (200) of any of paragraphs B-B3, wherein the operativelyinstalling (212) does not comprise penetrating a/the flexible sheet ofmaterial (154) of the vacuum bagging system (144) with the fluid lines(116).

C1. A bladder vent plug (300) for composite-manufacturing bladders(302), the bladder vent plug (300) comprising:

-   -   a main body (304) defining a main-body bore (306) extending        longitudinally through the main body (304);    -   a plug head (308) defining a plug-head bore (310) extending        longitudinally through the plug head (308) and longitudinally        aligned with the main-body bore (306), wherein the plug head        (308) is configured to be operatively coupled to a        composite-manufacturing bladder (302); and    -   an elongate conduit (312) extending from the plug head (308),        wherein the elongate conduit (312) is slidingly received within        the main-body bore (304);    -   wherein the main-body bore (306), the plug-head bore (310) and        the elongate conduit (312) are fluidically coupled and        collectively define a vent passage (314) extending through the        bladder vent plug (300).

C2. The bladder vent plug (300) of paragraph C1, wherein the plug head(308) is configured to close a hollow interior (338) of thecomposite-manufacturing bladder (302) except for communication betweenthe vent passage (314) of the plug head (308) and the hollow interior(338) of the composite-manufacturing bladder (302).

C3. The bladder vent plug (300) of any one of paragraphs C1-C2, furthercomprising a main-body sealing member (316) coupled to the main body(304) and engaged with the elongate conduit (312), wherein the elongateconduit (312) is configured to translate relative to the main-bodysealing member (316).

C3.1. The bladder vent plug (300) of paragraph C3, wherein the main-bodysealing member (316) comprises a wiper seal (318) disposed around themain-body bore (306).

C3.2. The bladder vent plug (300) of any one of paragraphs C3-C3.1,wherein the main-body sealing member (316) comprises a main-body O-ring(320) disposed around the main-body bore (306).

C4. The bladder vent plug (300) of any one of paragraphs C1-C3.2,further comprising an elongate-conduit sealing member (322) coupled tothe elongate conduit (312) and engaged with the main-body bore (306),wherein the elongate-conduit sealing member (322) is configured totranslate relative to the main-body bore (306).

C4.1. The bladder vent plug (300) of paragraph C4, wherein theelongate-conduit sealing member (322) comprises an elongate-conduitO-ring (324) disposed around the elongate conduit (312).

C5. The bladder vent plug (300) of any one of paragraphs C1-C4.1,further comprising at least one stroke limiter (326) fixed to the plughead (308), wherein the main body (304) further defines at least onestroke-limiter bore (328), and wherein the at least one stroke limiter(326) is slidingly received within the at least one stroke-limiter bore(328).

C5.1. The bladder vent plug (300) of paragraphs C5, wherein the at leastone stroke-limiter bore (328) defines a shoulder (330) configured tooperatively restrict the at least one stroke limiter (326) from fullyexiting the at least one stroke-limiter bore (328), such that the plughead (308) is restricted from being uncoupled from the main body (304).

C5.2 The bladder vent plug (300) of any one of paragraphs C5-05.1,wherein the at least one stroke limiter (326) comprises a head (332),and wherein the head (332) of the at least one stroke limiter (326) isconfigured to engage the shoulder (330) to restrict the at least onestroke limiter (326) from fully exiting the at least one stroke-limiterbore (328).

C5.3 The bladder vent plug (300) of any one of paragraphs C5-05.2,wherein the at least one stroke limiter (326) comprises two strokelimiters (326), and wherein the at least one stroke-limiter bore (328)comprises two stroke-limiter bores (328).

C5.4 The bladder vent plug (300) of paragraph C5.3, wherein the twostroke-limiter bores (328) are disposed on opposing sides of themain-body bore (306).

C6. The bladder vent plug (300) of any one of paragraphs C1-05.4,further comprising a vent connector (334) coupled to the main body (304)and in fluid communication with the main-body bore (306).

C6.1. The bladder vent plug (300) of paragraph C6, wherein the ventconnector (334) is configured to be coupled to a fluid line.

C6.2. The bladder vent plug (300) of any one of paragraphs C6-C6.1,wherein the vent connector (334) is longitudinally aligned with theelongate conduit (312).

C6.3. The bladder vent plug (300) of any one of paragraphs C6-C6.1,wherein the vent connector (334) is laterally offset from the elongateconduit (312).

C7. The bladder vent plug (300) of any one of paragraphs C1-C6.3,wherein the main body (304) and the plug head (308) have an at leastsubstantially similar cross-sectional shape.

C7.1. The bladder vent plug (300) of paragraph C7, wherein the main body(304), the plug head (308), and the composite-manufacturing bladder(302) have the at least substantially similar cross-sectional shape.

C8. The bladder vent plug (300) of any one of paragraphs C1-C6.3,wherein the main body (304) has a first cross-sectional shape, and theplug head (308) has a second cross-sectional shape different from thefirst cross-sectional shape of the main body (304).

C9. The bladder vent plug (300) of any one of paragraphs C1-C8, furthercomprising a sleeve (336) operatively coupled to the plug head (308) andthe main body (304), wherein the sleeve (336) is disposed between theplug head (308) and the main body (304) and extends around the elongateconduit (312).

C9.1. The bladder vent plug (300) of paragraph C9, wherein the sleeve(336) is corrugated.

C10. The bladder vent plug (300) of any one of paragraphs C1-C9.1,wherein the plug-head bore (310), the elongate conduit (312), and themain-body bore (306) are annular.

C11. The bladder vent plug (300) of any of paragraphs C1-C10, whereinthe main-body bore (306) comprises a main portion (307) within which theelongate conduit (312) is slidingly received, and a transverse exitportion (309) that extends transverse to the main portion (307).

C11.1. The bladder vent plug (300) of paragraph C11 in combination withthe system (100) of any of paragraphs A-A8, wherein the transverse exitportion (309) is in fluid communication with a/the vent line (140)extending through the layup mandrel (102), optionally through a/the facesheet (138) of the layup mandrel (102).

C12. The bladder vent plug (300) of any one of paragraphs C1-C11.1 incombination with the composite-manufacturing bladder (302) operativelycoupled to the plug head (308).

C12.1. The combination of paragraph C12, wherein thecomposite-manufacturing bladder (302) comprises a hollow interior (338),wherein the plug head (308) closes the hollow interior (338) of thecomposite-manufacturing bladder (302) except for the vent passage (314),and wherein the vent passage (314) is in fluid communication with thehollow interior (338) of the composite-manufacturing bladder (302).

As used herein, the terms “adapted” and “configured” mean that theelement, component, or other subject matter is designed and/or intendedto perform a given function. Thus, the use of the terms “adapted” and“configured” should not be construed to mean that a given element,component, or other subject matter is simply “capable of” performing agiven function but that the element, component, and/or other subjectmatter is specifically selected, created, implemented, utilized,programmed, and/or designed for the purpose of performing the function.It is also within the scope of the present disclosure that elements,components, and/or other recited subject matter that is recited as beingadapted to perform a particular function may additionally oralternatively be described as being configured to perform that function,and vice versa. Similarly, subject matter that is recited as beingconfigured to perform a particular function may additionally oralternatively be described as being operative to perform that function.

As used herein, the term “and/or” placed between a first entity and asecond entity means one of (1) the first entity, (2) the second entity,and (3) the first entity and the second entity. Multiple entries listedwith “and/or” should be construed in the same manner, i.e., “one ormore” of the entities so conjoined. Other entities optionally may bepresent other than the entities specifically identified by the “and/or”clause, whether related or unrelated to those entities specificallyidentified. Thus, as a non-limiting example, a reference to “A and/orB,” when used in conjunction with open-ended language such as“comprising,” may refer, in one example, to A only (optionally includingentities other than B); in another example, to B only (optionallyincluding entities other than A); in yet another example, to both A andB (optionally including other entities). These entities may refer toelements, actions, structures, steps, operations, values, and the like.

The various disclosed elements of apparatuses and steps of methodsdisclosed herein are not required to all apparatuses and methodsaccording to the present disclosure, and the present disclosure includesall novel and non-obvious combinations and subcombinations of thevarious elements and steps disclosed herein. Moreover, one or more ofthe various elements and steps disclosed herein may define independentinventive subject matter that is separate and apart from the whole of adisclosed apparatus or method. Accordingly, such inventive subjectmatter is not required to be associated with the specific apparatusesand methods that are expressly disclosed herein, and such inventivesubject matter may find utility in apparatuses and/or methods that arenot expressly disclosed herein.

1. A bladder vent plug, the bladder vent plug comprising: a main bodydefining a main-body bore extending longitudinally through the mainbody; a plug head defining a plug-head bore extending longitudinallythrough the plug head and longitudinally aligned with the main-bodybore, wherein the plug head is configured to be operatively coupled to acomposite-manufacturing bladder; and an elongate conduit extending fromthe plug head, wherein the elongate conduit is slidingly received withinthe main-body bore; wherein the main-body bore, the plug-head bore, andthe elongate conduit are fluidically coupled and collectively define avent passage extending through the bladder vent plug.
 2. The bladdervent plug of claim 1, wherein the plug head is configured to close ahollow interior of the composite-manufacturing bladder except forcommunication between the plug-head bore and the hollow interior of thecomposite-manufacturing bladder.
 3. The bladder vent plug of claim 1,further comprising a main-body sealing member coupled to the main bodyand engaged with the elongate conduit, wherein the elongate conduit isconfigured to translate relative to the main-body sealing member.
 4. Thebladder vent plug of claim 3, wherein the main-body sealing membercomprises a wiper seal disposed around the main-body bore.
 5. Thebladder vent plug of claim 3, wherein the main-body sealing membercomprises a main-body O-ring disposed around the main-body bore.
 6. Thebladder vent plug of claim 1, further comprising an elongate-conduitsealing member coupled to the elongate conduit and engaged with themain-body bore, wherein the elongate-conduit sealing member isconfigured to translate relative to the main-body bore.
 7. The bladdervent plug of claim 6, wherein the elongate-conduit sealing membercomprises an elongate-conduit O-ring disposed around the elongateconduit.
 8. The bladder vent plug of claim 1, further comprising atleast one stroke limiter fixed to the plug head, wherein the main bodyfurther defines at least one stroke-limiter bore, and wherein the atleast one stroke limiter is slidingly received within the at least onestroke-limiter bore.
 9. The bladder vent plug of claim 8, wherein the atleast one stroke-limiter bore defines a shoulder configured tooperatively restrict the at least one stroke limiter from fully exitingthe at least one stroke-limiter bore, such that the plug head isrestricted from being uncoupled from the main body.
 10. The bladder ventplug of claim 9, wherein the at least one stroke limiter comprises ahead, and wherein the head of the at least one stroke limiter isconfigured to engage the shoulder to restrict the at least one strokelimiter from fully exiting the at least one stroke-limiter bore.
 11. Thebladder vent plug of claim 1, further comprising a vent connectorcoupled to the main body and in fluid communication with the main-bodybore.
 12. The bladder vent plug of claim 11, wherein the vent connectoris configured to be coupled to a fluid line.
 13. The bladder vent plugof claim 1, wherein the main body and the plug head have an at leastsubstantially similar cross-sectional shape.
 14. The bladder vent plugof claim 1, further comprising a sleeve operatively coupled to the plughead and the main body, wherein the sleeve is disposed between the plughead and the main body and extends around the elongate conduit.
 15. Thebladder vent plug of claim 1, in combination with acomposite-manufacturing bladder operatively coupled to the plug head.16. The combination of claim 15, wherein the composite-manufacturingbladder comprises a hollow interior, wherein the plug head closes thehollow interior of the composite-manufacturing bladder except for thevent passage, and wherein the vent passage is in fluid communicationwith the hollow interior of the composite-manufacturing bladder.
 17. Asystem for assembling stiffened composite structures, the systemcomprising: a layup mandrel comprising an outer surface; and a stringerbladder positioned relative to the layup mandrel, the stringer bladdercomprising a hollow interior; and the bladder vent plug of claim 1operatively coupled to the stringer bladder, such that the bladder ventplug closes the hollow interior of the stringer bladder except for fluidcommunication between the vent passage and the hollow interior of thestringer bladder.
 18. The system of claim 17, wherein the layup mandrelcomprises a face sheet, wherein the main-body bore comprises a mainportion within which the elongate conduit is slidingly received, and atransverse exit portion that extends transverse to the main portion, andwherein the transverse exit portion is in fluid communication with avent line extending through the face sheet of the layup mandrel.
 19. Asystem for assembling stiffened composite structures, the systemcomprising: a layup mandrel comprising an outer surface; a network offluid lines, wherein the network of fluid lines is configured to beselectively and fluidically coupled to stringer bladders positionedrelative to the layup mandrel, and wherein the network of fluid linesextends through the layup mandrel; and a respective bladder vent plugoperatively coupled to each respective stringer bladder, such that therespective bladder vent plug closes a hollow interior of the respectivestringer bladder except for fluid connection to the network of fluidlines.
 20. The system of claim 19, wherein each respective bladder ventplug comprises: a main body defining a main-body bore extendinglongitudinally through the main body; a plug head defining a plug-headbore extending longitudinally through the plug head and longitudinallyaligned with the main-body bore, wherein the plug head is configured tobe operatively coupled to the respective stringer bladder; and anelongate conduit extending from the plug head, wherein the elongateconduit is slidingly received within the main-body bore; wherein themain-body bore (306), the plug-head bore, and the elongate conduit arefluidically coupled and collectively define a vent passage extendingthrough the respective bladder vent plug.